Germany's Constitutional Court on Tuesday ruled that the Lisbon Treaty was compatible with the country's constitution, but said some domestic laws needed tweaking before the treaty could be formally ratified.

Those laws concerned ensuring the German parliament in Berlin had a say in formulating EU decisions made in Brussels.

But the Christian Social Union of Bavaria (CSU), sister party to Merkel's CDU, said Friday they wanted even greater rights for the Bundestag and Bundesrat - the lower and upper houses of parliament respectively - enshrined in Germany's constitution.

The party also called for parliament to be enabled to take part in government decisions on EU matters, and wants the Constitutional Court to have the final word on interpreting the Lisbon Treaty.

"We generally want that the Bundestag and the Bundesrat must agree (to EU decisions before they impact Germany) … and we want that parliament has the right to complain if it feels its rights have been affected," said CSU chairman Horst Seehofer.

The Minister of State for Europe at the German Foreign Office, Guenter Gloser, warned the CSU against endangering the treaty's ratification schedule.

Merkel had said the necessary laws would be amended and the treaty passed before the September 27 federal election, but the latest demands from the CSU could prolong the ratification process.

The Bundestag is to hold special sessions on August 26 and September 8 to debate the legislation allowing the treaty to be ratified.

EU-wide ratification still awaits a second referendum on the treaty in Ireland, as well as approval by the eurosceptic presidents of the Czech Republic and Poland, which are awaiting the outcome of the Irish vote.

The Lisbon Treaty is a watered-down version of the EU constitution vetoed by French and Dutch voters in 2005. It aims to give the 27-nation bloc stronger leadership, a more effective foreign policy and a fairer decision-making system. All EU member states must approve the treaty for it to be formally adopted.

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Editor: Trinity Hartman